1. Field of Invention
The present invention relates to a method of scanning multiple tracks using an optical pickup using multiple optical spots, and more particularly, to a method of scanning multiple tracks using an optical pickup enabling high speed scanning without an increase in the rotational speed of a spindle motor by optimizing the interval between light spots and the number of tracks jumped.
2. Description of Related Art
Referring to FIG. 1 showing the configuration of a typical optical pickup device, a beam emitted from a light source 10 passes through a beam splitter 20, is converted into a parallel beam by a collimating lens 25 and is converged on a recording surface of a disk 1 by an object lens 30. Also, the beam reflected from the disk 1 proceeds toward a photodetector 50 by the beam splitter 20 and the photodetector 50 detects an RF (radio-frequency) information signal and an error signal from the reflected beam. Reference numeral 40 represents an astigmatism lens.
In the above optical pickup device, recording and reproduction of information are performed as a single beam emitted from the light source 10 follows a track spirally formed on a recording surface of the disk 1. When such an optical pickup device is adopted in a high speed multimedia subsystem, e.g., having a speed beyond 8.times., a spindle motor which enables rapid control of the RPM (revolutions per minute) is required to increase the high data transfer rate. Also, in the case when the high speed data transfer is achieved by increasing the RPM of the spindle motor, correction of the RF response characteristic in an actuator (not shown) of the optical pickup and conversion of the frequency characteristic of a servo circuit and an RF amplifying circuit are required.
Also, when a disk is driven at a CLV (constant linear velocity), the rotational speed of the disk must change rapidly while an optical pickup is moved radially across the disk resulting in increased torque and heat generation. Such heat affects each element of the optical pickup causing a deterioration in the signal.
In addressing the above problems, an optical pickup device is developed using a light source which emits multiple beams simultaneously to a plurality of tracks to thereby scan multiple tracks of a disk at once. Namely, N light spots emitted simultaneously from the light source in one disk rotation read information recorded on N tracks.
FIG. 2 shows a disk 1 and an enlarged portion thereof in which three beams concurrently emitted from a light source (not shown) form respective spots on the disk 1. Referring to the drawing, tracks 2 are formed spirally from the center of the disk 1 toward the outer circumference thereof. A groove 3 is formed between the tracks 2 and pits 2' corresponding to a recorded information signal.
In an optical pickup capable of scanning multiple tracks, high speeds cannot be readily achieved when the optical pickup is driven without consideration to the number of beams, the interval between beams, and a track jump to prevent double reproduction of a track. For instance, when first, second and third light spots 60a, 60b, and 60c emitted from the light source are first formed on first, second and third tracks 2a, 2b and 2c of the disk 1, respectively, as the disk rotates one time, the first light spot 60a, the second light spot 60b and the third light spot 60c move to the second track 2b, the third track 2c and a fourth track (not shown). Thus, the light spots are focused on the second and third tracks 2b and 2c repeatedly so that the efficiency in data reproduction is lowered.
FIG. 3 shows a graph indicating the relative speed ratio according to the number of multiple beams in performing multiple tracks scanning of a disk. Here, lines 101 through 106 represent the relative speed ratios according to the number of multiple beams for each of spindle motors having 2.times., 4.times., 6.times., 8.times., 10.times. and 12.times. speeds, respectively. As indicated in the drawing, when 3 beams are employed, the speed ratios of the 2.times. through 12.times. spindle motors improve by approximately twofold. Also, when there are 8 beams, the speed ratio of the 2.times. spindle motor (see line 101) becomes about 6 times faster and the speed ratio becomes about 2.5 times faster with respect to the 12.times. spindle motor (see line 106).
As mentioned above, in the conventional multiple track scanning method, since information on a portion of the tracks is repeatedly reproduced every rotation of the disk, the speed ratio does not increase linearly with an increase in the number of the multiple beams.